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Metformin Exposure During First Trimester Seen Safe for Fetus

Posted: Wednesday, October 25, 2006

Metformin taken by women with polycystic ovary syndrome (PCOS) during the first trimester of pregnancy does not appear to increase the risk of major fetal malformations, and may have a significant protective effect.

Metformin is used for the treatment of infertility in women with PCOS, yet the safety of the biguanide for the fetus has not been established, Dr. Gideon Koren of The Hospital for Sick Children in Toronto, Ontario, and colleagues point out. The other biguanide, phenformin, has been shown to be teratogenic.

Dr. Koren and colleagues conducted a meta-analysis of eight randomized, controlled studies of metformin taken during the first trimester of pregnancy by a total of nearly 500 women with either PCOS or diabetes.

From the pooled data, the malformation rate in the treatment group was 1.7% compared with 7.2% in disease-matched controls who did not receive metformin.

The researchers found that "after adjustment for publication bias, metformin was associated with a statistically significant protective effect of 57%" against major malformations in the fetus.

In their paper, the investigators caution that the data establishing safety of metformin in pregnancy is still limited. This study considered only major malformations of the fetus. Other studies assessing the incidence of spontaneous abortion, stillbirth, minor abnormalities, intrauterine growth retardation and preterm labor still need to be conducted.

Source: Diabetes In Control: Fertil Steril 2006;86:658-663